1. Field of the Invention
The present invention relates generally to the fields of cell physiology, neurology and neuro-oncology. More specifically, the present invention relates to a novel method of diagnosing and treating gliomas and meningiomas.
2. Description of the Related Art
Glial cells comprise a large proportion of the total cell population in the CNS. Unlike neurons, glial cells retain the ability to proliferate postnatally, and some glial cells still proliferate in the adult or aged brain. Uncontrolled glial proliferation can lead to aggressive primary intracranial tumors, the vast majority of which are astrocytomas, and therefore, of glial origin. Tumors of astrocytic origin vary widely in morphology and behavior, and, according to the 1993 WHO classification schema, can be separated into three subsets. Astrocytomas, the lowest grade tumors, are generally well-differentiated and tend to grow slowly. Anaplastic astrocytomas are characterized by increased cellularity, nuclear pleomorphism, and increased mitotic activity. They are intermediate grade tumors and show a tendency to progress to a more aggressive grade. Glioblastomas are considered the most aggressive, with poorly differentiated cells, vascular proliferation, and necrosis. Due to the common morphological heterogeneity of cells within a single tumor, such classification is not clear-cut and is somewhat unsatisfactory. The term "astrocyte-derived tumors" as used herein refers to astrocytomas. Meningiomas are tumor originating in the meninges.
Significant progress has been made in identifying physiologically important growth factors, receptors, and signal transduction pathways that control normal and malignant cell proliferation. It is now commonly accepted that growth factor binding leads to activation of oncogenes such as the ras/raf pathway, and ras in turn regulates gene expression through at least two mitogen-activated protein kinases. Interestingly, the ras/raf pathway is in crosstalk with the cAMP signaling cascade which is activated by numerous hormones and neurotransmitters.
Recent studies suggest that ion channels may function in regulating a cell's proliferative ability. For example, mitogen-stimulated lymphocytes show an upregulation in the expression of a high conductance potassium channel (15). In murine fibroblasts, activation of the ras/raf signaling cascade induces expression of a Ca.sup.2+ -activated K.sup.+ channel that appears to be essential in the cells' proliferative response (17). The idea that ion channel expression may be necessary for cell cycle progression is also supported by observations that pharmacological blockade of ion channels can inhibit cell proliferation. This has been demonstrated in a number of cell types including melanoma (28), breast cancer cells (41), brown fat cells (30), and also in several glial cell types such as Schwann cells (5), retinal glial cells (32) and astrocytes (29).
Untransformed glial cells from which glial tumors may originate have been extensively characterized electrophysiologically (37). Surprisingly, they appear to be liberally endowed with voltage- and ligand-activated ion channels for Na.sup.+, K.sup.+, Ca.sup.2+ and possibly Cl.sup.- ions. It is generally assumed that these ion channels perform homeostatic roles in the brain and may facilitate maintainance of K.sup.+ and possibly Na.sup.+ and Cl.sup.- ion concentrations in the extracellular space. In contrast to the numerous reports on ion channel expression and activity in nonneoplastic glial cells, electrophysiological properties of astrocytoma cells and the potential role of ion channels in growth control of astrocytomas remain largely unexplored. Inwardly rectifying K.sup.+ currents have been demonstrated in several established astrocytoma cell lines (4).
Gliomas cells are a very heterogeneous cell population that lack common antigens. Consequently, the prior art is deficient in the lack of effective means of identifying and treating malignant gliomas. The present invention fulfills this longstanding need and desire in the art.